Optical switch

Abstract

The present invention relates to optical switches in which switching occurs by changing the rotation of the plane of polarization by application of an externally applied control signal, particularly to magneto-optical switches controlling the port by which light emerges from the switch by externally-applied magnetic fields. The switches of the present invention function for randomly polarized input light, producing similarly randomly polarized light at the appropriate output port. Specific embodiments relate to 1×2 and 1×4 switches in both single pass and dual pass embodiments. Single pass embodiments are switches in which light passes through the optical components in one direction emerging at the appropriate output port depending on the desired switching. Dual pass embodiments are switches in which the light makes a forward and reverse traverse of the switch with total reflection. Dual pass switches typically reduce crosstalk without increasing the size of the switch. Single pass embodiments using two Faraday rotators are also disclosed for reducing crosstalk.

We claim:  
     
       1. A 1×2 optical switch comprising: 
       a) a light input port having a configuration to deliver input light to a first end of a first birefringent crystal, wherein said first birefringent crystal has a structure and orientation to separate said input light into a first ordinary beam and a first extraordinary beam and cause said first ordinary beam and said first extraordinary beam to emerge from the opposite second end of said first birefringent crystal separated by a walk-off distance; and,  
       b) a first half-wave plate and a second half-wave plate located such that said first half-wave plate intersects said first ordinary beam and said second half-wave plate intersects said first extraordinary beam, wherein said first half-wave plate has a structure and configuration so as to rotate the plane of polarization of said first ordinary beam by 45° and said second half-wave plate has a structure and configuration so as to rotate the plane of polarization of said first extraordinary beam by 45° in the opposite sense of said rotation of said first half-wave plate such that upon emerging from said first half-wave plate and said second half-wave plate said first ordinary beam and said first extraordinary beam have parallel polarizations; and,  
       c) a variable polarization rotator located so as to intersect said first ordinary beam and said first extraordinary beam following said first and said second half-wave plates, wherein said variable polarization rotator has the capability to rotate the plane of polarization by a first rotation or a second rotation as determined by the application of an external control signal to said variable polarization rotator, wherein said first rotation and said second rotation are positive and negative 45°; and,  
       d) a second birefringent crystal located so as to intersect said first ordinary beam and said first extraordinary beam at a first end thereof following said variable polarization rotator, wherein said second birefringent has a structure and orientation such that;  
       i) said first ordinary beam and said second ordinary beam pass through said second birefringent crystal undeflected when said control signal applied to said variable polarization rotator is such as to cause said first rotation and to emerge from the opposite, second end of said second birefringent as a second ordinary beam and a second extraordinary beam; and,  
       ii) said first ordinary beam and said second ordinary beam pass through said second birefringent crystal and emerge from the second, opposite face of said second birefringent crystal as the third ordinary beam and the third extraordinary beam, separated by said walk-off distance, when said control signal applied to said variable polarization rotator is such as to cause said second rotation; and,  
       e) a third half-wave plate having the location to intersect said second ordinary beam and having the structure and orientation so as to rotate by 90° the plane of polarization of light passing therethrough; and  
       f) a fourth half-wave plate having the location to intersect said second extraordinary beam and said third ordinary beam and having the structure and orientation to rotate by 0° the plane of polarization of light passing therethrough; and,  
       g) a fifth half-wave plate having the location to intersect said third extraordinary beam and having the structure and orientation to rotate by 90° the plane of polarization of light passing therethrough; and,  
       h) a third birefringent crystal located so as to intersect on a first end thereof said second and third ordinary beams and said second and third extraordinary beams following said third, fourth and fifth half-wave plates, and having the structure and orientation so as to recombine said second ordinary beam and said second extraordinary beam at a first light output port, and to recombine said third ordinary beam and said third extraordinary beam at a second light output port, wherein said first and said second light output ports are spatially separate.  
     
     
       2. A 1×4 optical switch comprising: 
       a) a light input port having a configuration to deliver input light to a first end of a first birefringent crystal, wherein said first birefringent crystal has a structure and orientation to separate said input light into a first ordinary beam and a first extraordinary beam and cause said first ordinary beam and said first extraordinary beam to emerge from the opposite second end of said first birefringent crystal separated by a walk-off distance; and,  
       b) a first half-wave plate and a second half-wave plate located such that said first half-wave plate intersects said first ordinary beam and said second half-wave plate intersects said first extraordinary beam, wherein said first half-wave plate has a structure and configuration so as to rotate the plane of polarization of said first ordinary beam by 45° and said second half-wave plate has a structure and configuration so as to rotate the plane of polarization of said first extraordinary beam by −45°; and,  
       c) a first variable polarization rotator located so as to intersect said first ordinary beam and said first extraordinary beam following said first and said second half-wave plates, wherein said first variable polarization rotator has the capability to rotate the plane of polarization by a first rotation or a second rotation as determined by the application of an external control signal to said first variable polarization rotator, wherein said first rotation and said second rotation are positive and negative 45°; and,  
       d) a second birefringent crystal located so as to intersect said first ordinary beam and said first extraordinary beam at a first end thereof following said variable polarization rotator, wherein said second birefringent has a structure and orientation such that;  
       i) said first ordinary beam and said second ordinary beam pass through said second birefringent crystal undeflected when said control signal applied to said variable polarization rotator is such as to cause said first rotation and to emerge from the opposite, second end of said second birefringent as a second ordinary beam and a second extraordinary beam; and,  
       ii) said first ordinary beam and said second ordinary beam pass through said second birefringent crystal and emerge from the second, opposite face of said second birefringent crystal as the third ordinary beam and the third extraordinary beam, separated by said walk-off distance, when said control signal applied to said variable polarization rotator is such as to cause said second rotation; and,  
       e) a third half-wave plate and a fourth half-wave plate located such that said third half-wave plate intersects said first ordinary and said first extraordinary beams following said first variable polarization rotator and said fourth half-wave plate intersects said second ordinary and said second extraordinary beams, wherein said first half-wave plate has a structure and orientation so as to rotate the plane of polarization of said first ordinary and extraordinary beams by 45° and said fourth half-wave plate has a structure and orientation so as to rotate the plane of polarization of said second ordinary and said second extraordinary beams by −45°; and,  
       f) a second variable polarization rotator located so as to intersect said first and second ordinary beams and said first and second extraordinary beams following said third and fourth half-wave plates, wherein said second variable polarization rotator has the capability to rotate the plane of polarization by a first rotation or a second rotation as determined by the application of an external control signal to said second variable polarization rotator, wherein said first rotation and said second rotation are positive and negative 45°; and,  
       g) a third birefringent crystal located so as to intersect said first and second ordinary beams and said first and second extraordinary beams at a first end thereof following said second variable polarization rotator, wherein said third birefringent has a structure and orientation such that;  
       1) said first and second ordinary beams and said first and second extraordinary beams pass through said third birefringent crystal undeflected when said control signal applied to said second variable polarization rotator is such as to cause said first rotation and to emerge from the opposite, second end of said third birefringent as third, fourth, fifth and sixth ordinary beams; and,  
       2) said first and second ordinary beams and said first and second extraordinary beams pass through said third birefringent crystal and emerge from the second, opposite face of said third birefringent crystal as the third, fourth, fifth and sixth extraordinary beams, separated by said walk-off distance, when said control signal applied to said second variable polarization rotator is such as to cause said second rotation; and,  
       h) a fifth half-wave plate having the location to intersect said third ordinary beam following said third birefringent crystal and having the structure and orientation to rotate by 90° the plane of polarization of light passing therethrough; and,  
       i) a sixth half-wave plate having the location to intersect said fourth ordinary beam and said third extraordinary beam following said third birefringent crystal and having the structure and orientation to rotate by 0° the plane of polarization of light passing therethrough; and,  
       j) a seventh half-wave plate having the location to intersect said fifth ordinary beam and said fourth extraordinary beam following said third birefringent crystal and having the structure and orientation to rotate by 90° the plane of polarization of light passing therethrough; and,  
       k) an eighth half-wave plate having the location to intersect said sixth ordinary beam and said fifth extraordinary beam following said third birefringent crystal and having the structure and orientation to rotate by 0° the plane of polarization of light passing therethrough; and,  
       l) a ninth half-wave plate having the location to intersect said sixth extraordinary beam following said third birefringent crystal and having the structure and orientation to rotate by 90° the plane of polarization of light passing therethrough; and,  
       m) a fourth birefringent crystal located so as to intersect on a first end thereof said third, fourth, fifth and sixth ordinary beams and said third, fourth, fifth and sixth extraordinary beams following said fifth, sixth, seventh and ninth half-wave plates, and having the structure and orientation so as to recombine said third ordinary beam and said fourth ordinary beam at a first light output port, and to recombine said fifth ordinary beam and said third extraordinary beam at a second light output port, and to recombine said fifth ordinary beam and said fourth extraordinary beam at a third light output port and to recombine said fifth extraordinary beam and said sixth extraordinary beam at a fourth light output port wherein said light output ports are spatially separate.